The present invention relates to an infrared filter. More particularly, it relates to an optical filter using a polyester film, especially, an optical filter having excellent transparency and workability and capable of intercepting the near infrared rays.
With start of BS digital high-vision broadcasting and spread of DVD players, request is rising for higher quality of display images. As a high quality display system that would supersede the presently prevailing CRT display, plasma display panel (hereinafter abbreviated as PDP) has begun to hit the market, partially to be used for public welfare, and is focusing the spotlight of attention.
PDP is of a system in which ultraviolet rays are radiated by electrical discharges in an inactive gas such as neon or xenon gas, and they are hit against a phosphor and converted into visible rays of RGB to cause luminescence. It is known, however, that such electrical discharges in an inert gas generate not only ultraviolet rays but also electromagnetic waves of various wavelengths which include light of a wavelength in the near infrared region which is often used for remote controls. If the light rays emitted from PDP are left as they are, they will cause wrong operation of remote controls to exert influence on the various remote-controlled devices such as household electrical appliances.
To the above problem, it has been proposed to mount an infrared filter, which can intercept the near infrared rays, on the front side of PDP. This infrared filter is generally manufactured by coating the surface of a highly transparent plastic film with a material comprising an infrared absorber, a polymer binder and other additives dissolved or dispersed in an organic solvent, and removing the solvent by drying (Japanese Patent Application Laid-Open (KOKAI) Nos. 11-95026, 11-305033, 11-326629, 11-326630, 2000-121828, etc.)
The infrared filters produced in the above references, however, have such disadvantages that since the surface of the infrared absorber-incorporated coating layer is highly flat for maintaining transparency, it is very difficult to wind up the film after coating and drying.